In the art of deposition of optically, electrically, chemically, magnetically or mechanically functional coatings, the physical vapour deposition (PVD) and the chemical vapour deposition (CVD) prevail. Physical vapour deposition relates to processes wherein the coating is built-up by a ballistic shower of the substrate with coating atoms. The coating atoms originate from a usually solid, sometimes liquid ‘target’. A preferred way of transferring the target material to the substrate is to bombard the target surface with high kinetic energy ions. A plasma of an inert gas—typically a noble gas such as argon—acts as a source of ions. The ions gain kinetic energy as they are accelerated towards the negatively biased target and eject the target material atoms towards the substrate. Such a process is called ‘sputter deposition’. The plasma can be confined in the vicinity of the target surface by means of magnetic fields originating from magnets placed at the side of the target opposite to the plasma side, a process referred to as ‘magnetron sputter deposition’. The target can be fed with a direct current, pulsed direct current or alternating current power source. When now a reactive gas is admitted to the argon, a compound layer will be formed at the surface of the substrate, a process referred to as ‘reactive magnetron sputter deposition’. In another variant of the ‘magnetron sputter deposition’, the magnetron can be made ‘unbalanced’ as opposed to ‘balanced’. With ‘unbalanced’ is meant that part of the magnetic field lines do not close on the target surface but fan out to the substrate. Electrons gyrating around these field lines then can reach the substrate and create a local plasma. Such a process is called ‘unbalanced magnetron sputtering’.
The ion current towards the substrate can be controlled by properly biasing the substrate with respect to the rest of the installation or by isolating the substrate making it floating with respect to the rest of the installation. In the latter case a self-bias will then develop that attracts ions to the substrate. Such a current of impinging ions leads to a further densification of the deposited layer, a process that is known as ‘ion plating’.
Chemical vapour deposition is in essence a process in which a gaseous precursor—usually a hydrocarbon—is excited so that radicals form that subsequently chemically react at the surface of the blank or already coated substrate. Excitation of the gaseous precursor can be achieved with a variety of means:                By thermal activation of the precursor. Heating of the gas can be achieved by heating the substrate or the walls of the reactor, or by using heater wires (hot wire CVD). Using heater wires has the additional advantage that thermally emitted electrons add to the activation degree of the precursor gas.        By irradiation with visible (photochemical vapour deposition), infrared or microwave electromagnetic waves.        Through excitement in a plasma (plasma activated CVD, PA CVD). To this end a noble gas atoms, usually argon, is mixed with the precursor gas in order to generate a plasma, that subsequently generates radicals in the precursor gas. The plasma can be excited by means of a radiofrequent electromagnetic field (typically 13.56 MHz).        A variant to this technique uses an unbalanced magnetron to fan out the plasma towards the substrate so that—in addition to the chemical deposition—ion plating occurs.Many times, different modes of activation are mixed in order to control coating properties or to enhance the speed of coating.        
For the purpose of this application, a process will be considered to be:                a PVD process as long as atoms are being dislodged from the target        a CVD process as long as precursor gas radicals are present in the apparatus        a ‘mixed process’ when target atoms are being dislodged while organic precursor molecules are present.        
More and more technologically important coatings are being produced involving complex stacks of layers deposited by PVD, reactive PVD and CVD and gradient layers that involve a mixture of both processes at the same time. One such a stack is e.g. described in WO 2005/014882 wherein first a Ti layer is deposited on a substrate (by means of magnetron sputtering), followed by a layer of TiN (by means of reactive magnetron sputtering), followed by a Ti layer that gradually changes from a TiC (mixed process) into a diamond like coating (DLC, chemical vapour deposition). The specific coatings are used as hard and wear resistant coatings in various applications.
The combination of both processes in one single apparatus poses many technological challenges to the equipment as the requirements of both processes are differing. For example, plasma sputtering processes normally take place at pressures between 0.01 and 100 Pa, whereas chemical vapour deposition processes can take place at pressures anywhere between 1 Pa and atmospheric pressure. Also the coating mechanism differs. In the PVD process, the flux of coating particles can be more or less directed towards the substrate. This necessitates the introduction of planetary carrousels to carry the substrates so that each and every spot on the sometimes complexly curved substrates is reached. The CVD process is based on diffusion and conformally coats the substrate. But it also tends to cover the whole deposition chamber including the sputtering target surface present in the chamber. This sputtering target surface gets covered with a CVD layer that disturbs the PVD process during the next use of the target.
The process control problems are particularly outspoken in the ‘mixed mode’ process wherein sputtering is combined with the administering of a mixture of an inert and precursor gas e.g. the sputtering of a Ti target in an acethylene (C2H2)-argon mixture to form a TiC layer. It turns out to be extremely difficult to reproducibly control the mixed process as a compound layer not only forms on the substrate, but also on the target which leads to undesirable phenomena like arcing (leading to the ejection of larger pieces out of a target) and instability of the process. Therefore a ‘target contamination’ problem exists in these processes.
Many reactors have been described that make possible ‘mixed processes’. There is for example the coater described in WO01/79585 that shows planar magnetrons mounted at the outer walls of an evacuable chamber. Other sources for excitement of precursor gasses are provided in the form of a low-voltage arc that can be drawn between a hot filament cathode and an anode. Densification of the layer formed is provided with a pulsed DC excitation between substrate and plasma.